Electrochemical behavior of the Cp*(dithiolato)Co(III) complex [(η₅-Cp*)Co(1,2-S₂C₂ B₁₀H₁₀-S,S′)] and its derivatives: The effect of the ligand on half-sandwich cobalt(III) complexes

Reaction of the 16-electron dithiolatocobalt, [(η⁵- Cp*)Co(Cab^S,S′)] (1) (Cab^S,S′=1, 2-S₂C₂B₁₀H₁₀-S,S′), with a ligand L (L=CN^tBu, PMe₃, PEt₃, PHPh₂) affords the 18-electron complexes [(η⁵- Cp*)Co(Cab^S,S′)(L)] (2) in high yield. The structures of 2 in solution were probed by NMR spectroscopy, and the solid-state structure of the diphenylphosphine derivative was established by single-crystal X-ray diffraction. Cyclic voltammetry of 1 shows that the complex undergoes a quasi-reversible one-electron oxidation and reversible reduction. The voltammetry of the corresponding 18-electron complex 2 was investigated rather extensively in terms of coordination and redox chemistry, in which the influence of the enhanced steric interaction between the bulky Cp* and incoming ligand could be observed. Cyclic voltammograms of alkylidiene or acetylene adducts of dithiolatocobalt complex 1, [(η⁵-Cp*)Co{η ³-(S,S′, C′)-SC₂B₁₀ H₁₀S(C′R₂)}] [C′R₂=CHSiMe ₃ (3a), HC=CPh (3b), (COOMe)C=C(COOMe) (3c)], are also included.